21 minute read
Face Masks and Respirators for the Dental Health Care Provider: A Review
Emma Bhaskar, BS
ABSRACCT As protocols and standards of personal protective equipment are changing in the time of COVID-19, dental health care providers must brief themselves on the appropriate products to keep them and their staff safe. This article reviews the current respiratory protection devices used to minimize the risk of SARS-CoV-2 infection.
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AUTHOR
Emma Bhaskar, BS, is a third-year dental student at the University of the Pacific, Arthur A. Dugoni School of Dentistry. She is from Monterey, Calif., and is a third-generation dentist in her family. She plans to attend a GPR or AEGD program and is particularly passionate about dental public and global health projects. Conflict of Interest Disclosure: None reported.
Medical masks were first developed and tested in the early 1900s with their use promoted in the 1920s to reduce infections. One of the first studies of the effectiveness of face masks demonstrated a zero incidence of diphtheria in the attendants who wore masks while caring for infected patients. In the 1930s, surgical teams began wearing masks to reduce postoperative infections. [1] Dentistry adopted the practice of universal precautions in the 1980s, mostly in response to the bloodborne human immunodeficiency virus (HIV) epidemic. Universal precautions are a set of protective guidelines set with the goal of preventing transmission of bloodborne pathogens from exposure to blood or other fluids containing blood by using gloves, masks, eye protection and gowns as protective clothing. In 1996, the Centers for Disease Control and Prevention (CDC) broadened the concept with standard precautions to include protection from bloodborne pathogens as well as pathogens in any bodily fluid, secreted or excreted. [2] The next level of precautions are specific to the pathogen and are called transmission-based precautions, including airborne precautions for severe acute respiratory syndrome (SARS), measles, varicella (chickenpox) and Mycobacterium tuberculosis. [3]
SARS-CoV-2 is a respiratory coronavirus that originated in Asia and has spread worldwide. The disease process is called novel coronavirus 2019 (COVID-19) and is caused by the coronavirus SARS-CoV-2. The World Health Organization (WHO) declared the COVID-19 disease a pandemic on March 11, 2020. COVID-19 is thought to spread person to person via respiratory transmission. Respiratory droplets are formed when an infected person talks, coughs or sneezes and the virus becomes suspended in a droplet for a period of time. This airborne transmission is thought to occur during close contact, specifically 6 feet or less. [4] This is of particular concern in the dental setting due to the close contact to patients and aerosols created during dental procedures. Dental procedures can create droplets when the dental health care provider (DHCP) uses aerosol-generating instruments such as a handpiece or cavitron. The DHCP should institute airborne precautions with respiratory protection devices while continuing to use standard precautions including handwashing, gowns, gloves and eye protection. This article reviews the current respiratory protection devices used to minimize the risk of SARS-CoV-2 infection.
There are two types of respiratory protection devices used in dentistry: the surgical mask, otherwise known as a face mask, and the respirator. Face masks are intended to prevent the spread of respiratory infections by the user with minimal protection for the user. Its function is to cover the mouth and nose, preventing the spread of viruses via large droplets created during talking, coughing or sneezing. The face mask protects the user from splashes of fluid and large airborne droplets but does not filter the smaller particles produced from dental procedures or a patient’s coughing and sneezing. [5] In addition, these masks fit loosely on the face and allow airborne pathogens and droplets to bypass the mask entirely through the gaps between the skin and mask. However, the presence of a face mask blocks handto-face/mouth/nose transmission of disease for the user. Face masks do not protect healthy people from respiratory infections. [6]
Respirators, such as the N95, are worn tightly around the health care provider’s mouth and nose to prevent the inhalation of airborne particles such as dust or infectious particles. Respirators are used to prevent infections such as tuberculosis, varicella [6] and, most recently, SARS.
Face Masks
A face mask, or surgical mask, is a loose-fitting, disposable, protective device that covers the mouth and nose of the user. The edges of the mask do not form a seal around the mouth and nose. Three types of surgical masks are rated by the American Society of Testing and Materials (ASTM) on the following criteria: bacterial filtration, submicron particulate filtration, differential pressure, resistance to penetration of synthetic blood and flammability. [7] The masks are designated as Level 1, Level 2 or Level 3 based on these testing results and are detailed in TABLE 1 ("ASTM Classifications, SEE TABLE IN FULL ISSUE OF THE JOURNAL) .
ASTM Level 1 masks provide lowlevel protection and can be used for administrative duties, previsit screening and nonfluid-producing appointments. Level 2 masks are used for lab and instrument processing tasks and low fluid-producing procedures such as simple restorative procedures, sealants and endodontics. If an N95 mask is not available, Level 3 can be used with a face shield for moderate to heavy spray and aerosol-producing procedures such as oral surgery, crown and bridge and the use of ultrasonic cleaners. [7] All three levels of masks have a Class 1 flame spread rating. [7] Masks that do not meet the ASTM testing criteria are considered “low-performance” face masks and should not be used in the dental office during the COVID-19 pandemic (TABLE 3, "Guide to the Selection of Common Face Masks and Respirators Used by DHCPs", SEE TABLE IN FULL ISSUE OF THE JOURNAL).
Respirators
Respirators are tightly fitted protective devices that cover the wearer’s mouth, nose and, in some cases, the entire face. These devices significantly reduce the risk of inhalation of airborne viruses and bacteria and can also filter dust particles, gases and vapors. There are three types of respirators available for use: the disposable or filtered facepiece respirator (FFR), the reusable elastomeric respirator with filter cartridges and the powered air-purifying respirator (PAPR).
Respirators are given an assigned protection factor (APF) by the Occupational Safety and Health Administration (OSHA). [8] The number varies with each type of respirator, with the higher number being more protective to the wearer. If a respirator has an APF of 10, one would expect it to reduce exposure of contaminant by a factor of 10. An APF of 1,000 will reduce the exposure of a contaminant by 1,000. [9] Factors such as environmental conditions, mask fit and the type of contaminant affect the protective factor of a respirator.
The N95 disposable filtering facepiece is the most commonly used respirator in health care. It is one of nine types of particulate disposable filtered respirators outlined in TABLE 2 ("Categorizations of the Nine Types of Particulate Disposable Filtered Respirators", SEE TABLE IN FULL ISSUE OF THE JOURNAL). These masks protect the wearer from biological threats such as viruses or bacteria but not gases or vapors. Each mask is categorized with a letter and number to signify its effectiveness. The respirators are rated as N, R or P for the mask’s protection against industrial oils (such as solvents or pesticides) that can degrade them. “N” masks are not resistant to oils, “R” masks are resistant to oils and masks labeled “P” are oil-proof. Because bacteria and viruses are not oil-based, there is little benefit to using the R- or P-rated masks in health care environments, but they are useful in the industrial setting. However, any of the nine disposable filtered respirators will protect the DHCP from biological threats and can be used. The numeric rating that follows each letter reflects the number of airborne particles that are filtered. At least 95% of airborne particles are filtered during a “worst-case” testing scenario with the most penetrating particle size. Respirators with 99% filtering capacity are rated 99, and those with 99.97% and higher receive the 100 rating. The National Institute for Occupational Safety and Health (NIOSH) is responsible for testing and rating respirators for use. All approved respirators have NIOSH markings and are listed on the NIOSH online database of approved respirators. Surgical N95 respirators are approved by the FDA as fluid resistant and referred to as N95s. Standard N95 respirators are not fluid resistant and the DHCP should use the N95s respirator if available. [10] The APF of N95 respirators is 10. [7]
Elastomeric respirators are face masks (full or half) that are made of natural or synthetic rubber and can be reused after disinfection of the unit. They have replaceable filters, adjustable straps and sealing edges for a tight fit. Elastomeric respirators offer an alternative to disposable N95 respirators, as they can be repeatedly used after disinfection. Thorough cleaning between patients is required with the manufacturer’s recommended disinfection solution, as improper cleaning can degrade or damage the device. Filters can be changed when clogged, soiled or contaminated. The respirator should be examined by a trained individual after each cleaning before use to ensure proper function and sanitation. [11] Filter ratings follow the same as disposable masks (N/P/R and 95/99/100); as with an N95 respirator, fit and seal are very important for the effectiveness of the respirator. Elastomeric respirators are generally not approved by the FDA as fluid resistant though they can provide equivalent protection of the N95 disposable filtered respirators. During shortages of respirators, the same elastomeric respirator can be used by multiple DHCP if it is properly cleaned, disinfected and inspected. The APF of half-mask elastomeric respirators is 10 and the full mask is 50. [7]
PAPRs are not commonly used in the dental setting but offer another option for the DHCP. PAPRs are air-purifying respirators that blow air through a highefficiency particulate air filter (HEPA) and then into the breathing zone of the user. A PAPR may have either a tight- or a loose-fitting full facepiece in a hood or helmet design. This airflow provides a higher level of protection for the user than either the N95 disposable respirator or elastomeric respirators. [10] PAPRs should be disinfected between uses and can be reused by others. Conventionally, filters are changed when they are soiled, damaged or there is reduced airflow, but in times of crisis or necessity, practices may demand cleaning and disinfecting the filter. [12] Some complications that may be involved with PAPR use include limited visual field and reduced ability to hear due to the loud blower noise. Concurrent use of an N95 with a PAPR has been shown to decrease inspired airborne particles even further. [13] PAPR systems have APF values of at least 25 for loose-fitting hoods and helmets, 50 for tight-fitting half masks and up to 1,000 for full-facepiece types and some loose-fitting hoods and helmets. [7,12]
The use of an N95 respirator or a respirator with a higher level of protection (PAPR, facepiece respirator or elastomeric respirator) is recommended for any aerosolgenerating procedure. If an N95 is not available, an ASTM Level 3 mask can be used with a full-face shield. If neither is available, it is not recommended to perform the aerosol-producing procedure.
Due to the shortage of N95 respirators, OSHA and the CDC have published guidelines for alternative non-NIOSHapproved respirators and filters certified in other countries as a replacement for the N95 respirators. These approved alternative respirators are listed on the CDC website and include, but are not limited to, the KN/KP95 from China, P2 from Australia, Special 1st from Korea and N95 from Mexico. [17] Many of these alternative respirators utilize the ear loop design, which may make a proper fit more difficult. [18] OSHA and the CDC consider the use of homemade masks or modified masks in the care of patients as a last resort. Homemade masks are not considered acceptable personal protective equipment (PPE) because the ability to protect the user is unknown. The use of face shields is recommended with all masks and respirators and is especially necessary with alternative masks and respirators. [19]
Fit Test
OSHA requires that before an employee is required to use any respirator with a negative or positive pressure tight-fitting facepiece, the employee must be fit tested with the same make, model, style and size of respirator that will be used. The two approved tests that OSHA accepts are the qualitative fit test (QLFT) and the quantitative fit test (QNFT). Traditionally, a fit test must be done annually with all employees who are required to wear tight-fitting respirators, but as of March 2020, the OSHA enforcement will exercise discretion concerning the annual fit testing requirements in response to the shortage of filtering facepiece respirators due to COVID-19 as long as employers have made “good-faith efforts” to comply with fit testing standards. [20] A fit test is not required for PAPRs with loose-fitting headgear such as hoods and helmets. The QLFT is usually performed for halfface respirators like the N95 mask. [21]
As discussed, surgical masks often fit loosely, functioning to prevent the wearer from spreading large sprays and droplets and from hand-to-face contact but fail to protect the wearer from smaller airborne droplets. When using respirators, a key component for protection is providing the wearer with an appropriate fit test to improve the efficacy of the respirator in use. In a study that focused on respirator efficacy and fit performance, researchers found that even when using respirators with high filtering capacity, 10% to 40% of particles penetrated a facial seal as a result of improper fit. For aerosols containing organisms with a low infectious dose, such as tuberculosis, the level of facial seal leakage would not prevent exposure during a brief encounter with an infected patient generating an abundant amount of aerosol. [22] Due to close proximity to patients and high aerosol concentrations generated by routine dental procedures, the DHCP should demonstrate strict airborne precautions to avoid exposure.
A respirator’s assigned protection factor (APF) is only valid if it fits correctly. []7 Respirator fit is important because it involves concerns such as seal, compatibility and stability. A seal ensures that the respirator is being worn properly and protects the wearer from aerosol exposure. A mask cannot properly seal if the wearer has any facial hair, including beards, mustaches or even stubble, so the wearer must be clean-shaven when present for a fit test. [21] Compatibility ensures that other PPE, such as eye shields and hard hats, will not disrupt the effectiveness of the respirator being worn. For this reason, any additional PPE that will be worn with the mask should be worn during the fit test. And lastly, stability determines the respirator’s ability to retain a seal while the wearer is in motion.
The QLFT may only be used to fit test negative-pressure, air-purifying respirators such as the N95 mask. The test relies on the subject to be able to detect leakage into the mask with smell or taste. Rather than measuring the amount of leakage, it is a pass/fail test assessing the user’s ability to detect isoamyl acetate, saccharin, Bitrex and irritant smoke. The isoamyl acetate (banana smell) test is an odor detection test, the saccharin (sweet) and Bitrex (bitter) tests are taste-detection tests and the irritant smoke test relies on an involuntary irritation (cough) response by the wearer. In order for a QLFT test to be meaningful, care must be taken so that the substances may only enter through a facial leak, meaning that the respirator must have the capacity to filter all substances. Isoamyl acetate is only for testing respirators with organic vapor cartridges, and the irritant smoke can only be used for respirators with level 100 particulate filters. Saccharin and Bitrex can test respirators with particulate filters of any class. Each QLFT method uses each of these seven exercises performed for one minute: normal breathing, deep breathing, moving head side to side, moving head up and down, bending over or jogging in place, talking and then normal breathing once again. [21] The test must be done with the respirator the user will use in the office because the fit test is respirator specific.
The QNFT can be used to fit test any tight-fitting respirator, usually a full-face respirator. The test involves using an instrument to measure leakage around the face seal and produces a numerical result called a fit factor. A fit factor is defined as the ratio of the test agent concentration outside the respirator to the test agent concentration inside the respirator or the ratio of total airflow through the respirator to the airflow through face seal leaks. OSHA accepts three QNFT protocols. The first accepted protocol is generated aerosol, which uses a nonhazardous aerosol such as corn oil generated in a test chamber. The second is a condensation nuclei counter (CNC), which uses environmental aerosol and does not require a test chamber. The third is a controlled negative pressure test, which creates a vacuum by temporarily cutting off air. QNFT uses the same seven exercises described in the QLFT plus an additional test where the participant “grimaces” (smiles or frowns) for 15 seconds. A fit factor of at least 100 is required for half-mask respirators and a minimum fit factor of 500 for a fullfacepiece negative pressure respirator. [7,21]
Different types of N95 respirators should be available for testing if there is a failure of the fit test due to respirator contour. Any change in facial contours including extensive dental work, weight change, facial surgery or facial scarring will dictate a new fit test.
PPE in the Dental Setting
Once employees in a dental office have been properly fit tested for a respirator, the CDC recommends that the DHCP receives education on factors including when to use specific PPE, what PPE is necessary for each procedure, how to properly don, wear, doff and dispose of their protective equipment and the limitations of their PPE. The CDC recommends that when treating patients who are assumed to be noncontagious during an aerosol-generating procedure, the DHCP should use an N95 respirator or other respirator with a higher level of protection. [23]
When donning a face mask or a respirator, one must wash their hands thoroughly and secure the top strap or tie on the crown of the head and the bottom strap on the base of the neck. Face masks with ear loops may be worn by placing the loops securely around the ears. Users should perform a seal check with every use of their respirator. Positive pressure seal checks are done with respirators without valves. After donning the respirator, place hands over respirator amd exhale gently; the fit is considered acceptable if positive pressure is built up in the mask without leakage. Any air movement at the borders of the respirator, fogging of glasses or lack of pressure is a failure. [24] After completion of care, the DHCP should perform hand hygiene once again and exit the patient care area to remove their face mask or respirator. A face mask may be removed by pulling it away from the face by the ear loops or ties without touching the front of the mask. A respirator should be removed by pulling the bottom strap up over the head, followed by the top strap, and pulling the respirator away from the face without touching the front of the respirator. The DHCP should perform hand hygiene once more after removing their face mask or respirator. [23]
Major distributors have reported a shortage of PPE in the U.S., specifically face masks and respirators. The CDC has developed a series of guidelines to optimize PPE supplies in the workplace, including decontamination strategies and a PPE Burn Rate Calculator that offices may use to ration their supplies. [25] In times of contingency, the reuse of N95 respirators may be considered. However, it is unclear how reuse affects the respirator function and contamination. In general, respirators contaminated with blood, saliva or respiratory secretion should be discarded after aerosol procedures. Other used respirators can be hung in designated areas or stored in a paper bag between uses to minimize cross-contamination. [26] Ultraviolet germicidal irradiation, vaporous hydrogen peroxide and moist heat have been discussed as effective methods of decontamination. The use of dry heat, autoclave, isopropyl alcohol, soap, microwave, bleach, disinfectant wipes and ethylene oxide should not be used due to degradation to the mask or harm to the wearer. The manufacturers of N95 respirators should be contacted for reuse guidance and recommendations. [27]
Respirators may also be used past their shelf life in times of limited supply. However, the expired respirator may not perform at the same capacity once past its manufacturer’s designated expiration date. The straps may degrade, causing the fit and seal to be unsatisfactory. [28] It is recommended that expired respirators only be used for nonaerosol-producing procedures.
Physiologic Effects
Heart rate, temperature, humidity and subjective comfort are influenced by the wearing of different kinds of face masks and respirators. The temperature inside of a mask increases with exercise and movement, which in many wearers may give the perception of breathing resistance, leading to an increased breathing rate. [29] High breathing rates make it difficult to take in sufficient oxygen, which triggers the sympathetic nervous system to increase heart rate. This chain of events can lead the wearer to feel fatigued, faint and uncomfortable.
While both surgical masks and respirators can cause these effects, notable differences have been made between N95 and surgical masks in terms of comfort and altered sensations. Overall humidity, skin temperature inside the mask, perceptions of breathing resistance and discomfort have been found to be higher among N95 than surgical masks. [29] Headaches have also been noted to have a higher incidence following the extended (> 4hr) use of N95 masks due to increased respiratory rate and discomfort. 30 Surgical masks, with higher moisture and air permeability, are thinner than N95 respirators, making them more breathable and in turn more comfortable for the wearer. All these factors may be reasons for reluctance to wear respirators in the workplace. However, the respirator’s superior fit and filtration should override these inconveniences.
Conclusion
A thorough understanding of the types and uses of face masks and respirators in the dental office is paramount for the DHCP’s respiratory health. In addition, every dental practice should institute a respiratory protection program that includes mitigation strategies, respirator selection, medical evaluations, fit testing, training and maintenance of respirators. [31] A respiratory protection program, along with the PPE required for standard and airborne precautions, will ensure the safety of the dental team and dental patient.
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THE AUTHOR, Emma Bhaskar, BS, can be reached at e_bhaskar@u. pacific.edu.
